The proposed resonance Raman and other spectroscopic studies are directed at the understanding of structures of the metal ion environments in metalloproteins and metalloenzymes. Of particular interest in these investigations are the biological molecules which work in concert with molecular oxygen: the respiratory proteins, hemocyanin and hemerythrin, and the oxidases and dioxygenases. The proposed project period includes structural and mechanistic studies on the non-heme-iron enzyme, ribonucleotide reductase. It is of paramount importance to elucidate the structure of this metalloenzyme as it presently represents only the second example of a biological molecule that possesses an antiferromagnetically-coupled pair of iron atoms next to the example afforded by hemerythrin. Iron coordination in the natural chelator, schizokinin, will be pursued. In addition, some studies on non-metallic chromophores are underway, such as the interaction of dye-labeled molecules binding to acetylcholine receptor or the characterization of resonant scattering from FAD and/or FMN containing systems. Throughout our studies, structural characterization of model complexes are pursued to assist in the definition of ligation and geometry of the naturally-occurring metal sites in biomolecules.